Inflatable air-bag

ABSTRACT

An inflatable airbag is disclosed which defines an inflatable chamber. The airbag generally includes an inner elastic membrane provided in the peripheral wall of the airbag and a vent-hole formed through the elastic membrane. An outer membrane is provided on the outside of the airbag that extends across at least part of the inner membrane and the vent-hole. The outer membrane defines a pucker over the inner membrane and the vent-hole. The pucker is open so as to define an outlet flow path from the vent-hole when the inner membrane is spaced from the pucker. The inner membrane is configured to stretch and seal against the pucker around the vent-hole when the internal pressure within the inflatable chamber exceeds a predetermined value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit and priority of GB 0324291.4, filed16 Oct. 2003. This application is a National Stage of InternationalApplication No. PCT/SE2004/001470, filed 14 Oct. 2004. The entiredisclosures of the above applications are incorporated herein byreference.

FIELD

THE PRESENT INVENTION relates to an inflatable airbag, and moreparticularly to an airbag to be mounted in a motor vehicle as a safetydevice to provide cushioning to an occupant of the vehicle in the eventthat the vehicle is involved in a crash situation.

BACKGROUND

It is known to vent an airbag provided for use in a motor vehicle toprotect an occupant of the vehicle in the event that an accident shouldoccur, especially if the airbag is of the type intended to provideprotection in the event that a front impact should occur.

An airbag that is intended to provide protection in the case of a frontimpact is generally located so that, when inflated, the airbag ispositioned in front of the occupant to be protected. Such airbags aretypically provided within the dashboards or steering wheels of motorvehicles to protect the occupants from impact with the hard structuresbehind the airbag.

During a front impact, the motor vehicle decelerates suddenly. Due toinertia, the occupant of the vehicle tends to continue moving, and thusthe occupant of the vehicle is, in effect, moving forwardly relative tothe rest of the vehicle. The function of the airbag is to decelerate theoccupant, preferably in such a way that the occupant suffers no injury.The airbag must be inflated very swiftly and thus, typically, containsrelatively high pressure gas. If the airbag were not vented, thenbecause of the gas pressure within it, the airbag would not deceleratethe occupant gently, but instead would stop the occupant extremelyswiftly and hence may injure the occupant. Thus, many airbags areprovided with vent-holes formed in them so that, when the airbag isstruck by the occupant, gas can escape from the airbag through thevent-hole or holes, so that the airbag serves the function ofdecelerating the occupant more gently, to avoid such injury.

In many cases, it has been found to be desirable to control the degreeof venting. For example, in a low load accident situation, such as aslow speed accident or an accident in which the occupant to be protectedby the airbag is of relatively low mass, then a relatively high degreeof venting is appropriate to safely decelerate the occupant. However, ina high load accident, for example a high speed accident, or an accidentin which the seat occupant has a relatively high mass, and hence highinertia, a lower degree of venting is often desirable in order toprevent the seat occupant “striking through” the airbag and sufferinginjury from impact with dashboard or steering wheel structures locatedbehind the airbag.

SUMMARY

It is therefore desirable to provide an effective means to selectivelyclose a vent-hole provided in an airbag, depending upon the loadconditions of the accident situation.

The present invention seeks to provide an improved inflatable airbag.

According to the present invention, an inflatable airbag defines aninflatable chamber for fluid connection to an inflator having an elasticinner membrane provided in the peripheral wall of the airbag; avent-hole formed through the elastic membrane; and an outer membraneprovided on the outside of the airbag so as to extend across at leastpart of the inner membrane and the vent-hole. The outer membrane definesa pucker over the part of the inner membrane, the pucker being open soas to define an outlet flow path from the vent-hole when the part of theinner membrane is spaced from the pucker. The inner membrane stretchesand seals against the pucker, around the vent-hole, when the internalpressure within the inflatable chamber exceeds a predetermined value.

Preferably, the inner membrane is made of silicone.

Advantageously, the inner membrane has more than one vent-hole.

Conveniently, the airbag is made of fabric and the inner membrane issecured across an aperture formed in the fabric.

Preferably, the inner membrane is stitched to the fabric of the airbag.

Advantageously, the inner membrane is glued to the fabric of the airbag.

Conveniently, the outer membrane comprises a strip of fabric stitched tothe airbag.

Preferably, the pucker takes the form of a loose fold across the outermembrane and is open at both of its ends.

Advantageously, the outer membrane is integral with the material of theairbag defining the inflatable chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the invention may be more readily understood, and so thatfurther features thereof may be appreciated, an embodiment of theinvention will now be described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a schematic sectional view taken through part of an airbag inaccordance with the present invention illustrating a vent-holearrangement;

FIG. 2 is a view from above of the vent-hole arrangement illustrated inFIG. 1;

FIG. 3 is a view corresponding generally to that of FIG. 1, illustratingthe vent-hole arrangement during a low-load impact situation; and

FIG. 4 is a view corresponding generally to that of FIG. 3, butillustrating the vent-hole arrangement in a high-load impact situation.

DETAILED DESCRIPTION

Referring initially to FIGS. 1 and 2 of the accompanying drawings, thereis illustrated an inflatable airbag 1 which comprises an envelope offlexible material 2 such as, for example, woven fabric material, whichdefines an inflatable chamber 3 for fluid connection to an inflator (notillustrated) in a manner known per se. The fabric 2 defines a peripheralwall of the airbag 1.

An aperture 4 is provided through the fabric 2 of the airbag 1, acrosswhich an elastic inner membrane 5 is provided. It will be seen from FIG.2, that in the specific embodiment illustrated the inner membrane 5 issubstantially circular, although it will be appreciated that inalternative embodiments, different shapes of inner membrane could beused. In the preferred embodiment of the invention, the inner membrane 5is made of silicone. It will be seen that the inner membrane 5 issecured to the fabric 2 of the airbag 1 around its periphery. The innermembrane 5 may be secured to the fabric 2 by any convenient means suchas, for example, by way of a line of peripheral stitching 6.Alternatively, or additionally, the inner elastic membrane 5 can beglued to the fabric 2 of the airbag 1.

A small vent-hole 7 is provided through a substantially central part ofthe inner membrane 5.

An outer membrane 8 is provided on the outside of the airbag 1, locatedon the opposite side of the inner membrane 5 to the inflatable chamber3. The outer membrane 8 preferably takes the form of a strip of fabricmaterial, as illustrated in FIG. 2. However, it is envisaged that othermaterials, instead of fabric, could be used for the outer membrane 8provided the material has a lower degree of elasticity than the innermembrane 5. The outer membrane 8 illustrated in FIG. 2 is of generallyelongate rectangular form and it will be seen that the membrane 8 issecured to the peripheral wall of the airbag 1 by lines of stitching 9.However, it is also envisaged that the outer membrane 8 could be part ofthe airbag fabric 2.

The strip of fabric defining the outer membrane 8 extends across atleast the central region of the inner elastic membrane 5, and asillustrated in FIGS. 1 and 2, the ends of the outer membrane 8 arestitched to the airbag 1 on opposed sides of the inner membrane 5. Theouter membrane 8 is configured so as to define a pucker 10 in the formof a loose fold or bulge which is located above the vent-hole 7 providedthrough the inner membrane 5. As illustrated most clearly in FIG. 2, thepucker 10 extends transversely across the fabric strip defining theouter membrane 8 and is open at both ends so as to define a gas flowpath from the vent-hole 7 to atmosphere (as illustrated by arrows 11, 12in FIG. 2).

FIG. 1 illustrates the vent-hole arrangement in a relaxed condition inwhich the elastic membrane 5 is stretched lightly across the aperture 4provided in the fabric 2.

FIG. 3 illustrates the vent-hole arrangement in a condition which itadopts during a low-load impact situation, for example a slow speedaccident and/or an accident involving a relatively low mass passenger.In this type of accident situation, as the passenger impacts with theairbag 1 under relatively low-load, the internal gas pressure within theairbag 1, following initial inflation of the airbag 1, is caused toincrease slightly and hence, as illustrated, the inner elastic membrane5 is caused to stretch and deform outwardly by a small amount. In thislow-load impact situation, it will be seen that the degree ofdeformation caused to the inner elastic membrane 5 by the internal gaspressure of the airbag 1 is small enough to ensure that the vent-hole 7is always spaced from the inner surface of the pucker 10, which meansthat gas is allowed to vent from the inflatable chamber 3, through thevent-hole 7 and out from underneath the pucker 10, for example asillustrated by arrow 13 in FIG. 3.

In contrast to the situation illustrated in FIG. 3, FIG. 4 illustratesthe vent-hole arrangement in a condition that it adopts during ahigh-load impact situation, such as, for example, a higher speed crash,and/or a crash involving an occupant having a higher mass. It should beappreciated that in such an impact situation, the passenger of the motorvehicle to be protected by the airbag 1 will have a higher degree ofinertia, which will mean that a higher load is applied to the airbag 1as the occupant impinges on the airbag 1. This means that the internalgas pressure of the inflatable chamber 3 will increase more quickly andto a higher level than in the case illustrated in FIG. 3. The innerelastic membrane 5 responds to this higher increase of gas pressure, andis configured such that, if the internal gas pressure of the inflatablechamber 3 exceeds a predetermined value, then the central region of theinner elastic membrane 5 stretches and bears against the pucker 10, andeffectively seals against the undersurface of the pucker 10, around thevent-hole 7. This, therefore, closes the vent-hole 7 and preventsoutflow of gas from the inflatable chamber 3, thereby preventing furthercollapse of the airbag 1 and hence preventing “strike-through” of theseat occupant with respect to the airbag 1.

It should be appreciated that the above-described invention provides asimple vent arrangement which permits venting in a low-load condition,but which prevents venting in a high-load condition in order to preventprotection to a passenger of the motor vehicle from “strike-through”injuries.

In the present specification “comprises” means “includes or consists of”and “comprising” means “including or consisting of”.

The features disclosed in the foregoing description, the followingclaims, or the accompanying drawings, expressed in their specific formsor in terms of a means for performing the disclosed function, or amethod or process for attaining the disclosed result, as appropriate,may separately, or in any combination of such features, be utilized forrealizing the invention in diverse forms thereof.

1. An inflatable airbag defining an inflatable chamber for fluidconnection to an inflator, the airbag comprising: an elastic innermembrane provided in a peripheral wall of the airbag; a vent-hole formedthrough the elastic inner membrane; and an outer membrane provided onthe outside of the airbag so as to extend across at least part of theinner membrane and the vent-hole, the outer membrane defining a puckerover the part of the inner membrane, the pucker being open so as todefine an outlet flow path from the vent-hole when the part of the innermembrane is spaced from the pucker; the inner membrane being configuredto stretch and seal against the pucker, around the vent-hole, wheninternal pressure within the inflatable chamber exceeds a predeterminedvalue, wherein the pucker takes the form of a loose fold across theouter membrane and is open at both of its ends.
 2. The airbag accordingto claim 1, wherein the inner membrane is made of silicone.
 3. Theairbag according to claim 1, wherein the inner membrane has more thanone vent-hole.
 4. The airbag according to claim 1, wherein the airbag ismade of fabric and the inner membrane is secured across an apertureformed in the fabric.
 5. The airbag according to claim 4, wherein theinner membrane is stitched to the fabric of the airbag.
 6. The airbagaccording to claim 4, wherein the inner membrane is glued to the fabricof the airbag.
 7. The airbag according to claim 1, wherein the outermembrane comprises a strip of fabric stitched to the airbag over thevent-hole for creating an outlet flow path from the vent-hole toopen-to-atmosphere ends of the pucker.
 8. A flow regulation valve incombination with an airbag having a deflatable inner chamber, the valvecomprising: an elastic inner membrane fastened to an interior of theairbag; a vent-hole formed through the inner membrane; an outer membranefastened to an exterior of the airbag so as to extend across at leastpart of the vent-hole; and a pucker in the form of a loose fold acrossthe outer membrane and over the vent-hole for creating an outlet flowpath from the vent-hole to open-to-atmosphere ends of the pucker whenthe inner membrane is spaced from the pucker, and for closing the outletflow path when an internal pressure within the deflatable inner chamberexceeds a predetermined value.
 9. The valve according to claim 8,wherein the inner membrane is made of silicone.
 10. The valve accordingto claim 8, wherein the inner membrane has more than one vent-hole. 11.The valve according to claim 8, wherein the airbag is made of fabric andthe inner membrane is secured across an aperture formed in the fabric.12. The valve according to claim 11, wherein the inner membrane isstitched to the fabric of the airbag.
 13. The valve according to claim11, wherein the inner membrane is glued to the fabric of the airbag. 14.The valve according to claim 8, wherein the outer membrane comprises astrip of fabric stitched to the airbag.
 15. A flow regulation valve incombination with an airbag having a deflatable inner chamber, the valvecomprising: an airbag material defining the deflatable inner chamber ofthe airbag; an inner membrane secured to an inner surface of the airbagmaterial; a vent through a central part of the inner membrane forallowing air to be expelled from the deflatable inner chamber of theairbag; and an outer membrane secured to an outer surface of the airbagmaterial creating a raised pucker over the vent-hole, wherein the innermembrane seals against the outer membrane preventing air from expellingthrough the vent-hole when an inner air pressure exceeds a predeterminedthreshold; wherein the raised pucker creates an outlet flow path fromthe vent-hole to at least one open-to-atmosphere end of the outermembrane when the inner membrane is spaced from the raised pucker. 16.The valve according to claim 15, wherein the inner membrane includesmore than one vent-hole.
 17. The valve according to claim 15, whereinthe inner membrane is one of stitched and glued to the airbag material.18. The valve according to claim 15, wherein the inner membrane materialis one of elastic, fabric, and silicone.
 19. An inflatable airbagdefining an inflatable chamber for fluid connection to an inflator, theairbag comprising: an elastic inner membrane provided in a peripheralwall of the airbag; a vent-hole formed through the elastic innermembrane; and an outer membrane provided on the outside of the airbag soas to extend across at least part of the inner membrane and thevent-hole, the outer membrane defining a pucker over the part of theinner membrane, the pucker being open so as to define an outlet flowpath from the vent-hole when the part of the inner membrane is spacedfrom the pucker; the inner membrane being configured to stretch and sealagainst the pucker, around the vent-hole, when internal pressure withinthe inflatable chamber exceeds a predetermined value, wherein the outermembrane comprises a strip of fabric stitched to the airbag over thevent-hole for creating an outlet flow path from the vent-hole toopen-to-atmosphere ends of the pucker.